The present invention relates generally to the field of subterranean exploration and drilling and, more particularly, to a method and system for enhanced access to a subterranean zone.
Subterranean deposits of coal, whether of xe2x80x9chardxe2x80x9d coal such as anthracite or xe2x80x9csoftxe2x80x9d coal such as lignite or bituminous coal contain substantial quantities of entrained methane gas. Limited production and use of methane gas from coal deposits has occurred for many years. Substantial obstacles, however, have frustrated more extensive development and use of methane gas deposits in coal seams. The foremost problem in producing methane gas from coal seams is that while coal seams may extend over large areas, up to several thousand acres, the coal seams are fairly shallow in depth, varying from a few inches to several meters. Thus, while the coal seams are often relatively near the surface, vertical wells drilled into the coal deposits for obtaining methane gas can only drain a fairly small radius around the coal deposits. Further, coal deposits are not amendable to pressure fracturing and other methods often used for increasing methane gas production from rock formations. As a result, once the gas easily drained from a vertical well bore in a coal seam is produced, further production is limited in volume. Additionally, coal seams are often associated with subterranean water, which must be drained from the coal seam in order to produce the methane.
Horizontal drilling patterns have been tried in order to extend the amount of coal seam exposed to a drill bore for gas extraction. Traditional horizontal drilling techniques, however, require the use of a radiused well bore which presents difficulties in removing the entrained water from the coal seam. The most efficient method for pumping water from a subterranean well, a sucker rod pump, does not work well in horizontal or radiused bores.
Additionally, prior systems generally require a fairly large and level surface area from which to work. As a result, prior methods cannot be used in Appalachia and other very hilly terrain where the largest flat land area may be a wide roadway. Thus, less effective methods must be used, leading to production delays that add to the expense associated with degasifying a coal seam.
The present invention provides a method and system for accessing subterranean zones from a limited surface area that substantially eliminates or reduces the disadvantages and problems associated with previous systems and methods. In particular, an articulated well bore with a well bore pattern in a subterranean seam extends to cavity wells in communication with the well bore pattern in the seam. The well bore patterns provide access to a large subterranean area while the cavity wells allow entrained water, hydrocarbons, and other deposits collected by the well bore pattern to be efficiently removed and/or produced.
In accordance with one embodiment of the present invention, a subterranean well bore pattern for accessing an area of a subterranean zone from the surface includes a first well bore extending from a surface well bore substantially defining a first end of the area in the subterranean zone to a distant end of the area. The pattern also includes a plurality of lateral well bores extending outwardly from the first well bore. The lateral well bores are configured such that a distance from an end of a lateral well bore to the surface well bore is substantially equal for each of the lateral well bores.
In accordance with another embodiment of the present invention, a method for accessing a subterranean zone from the surface includes forming a first well bore pattern in the form of a first substantially quadrilateral area. The first well bore pattern extends from a surface well bore. The method also includes forming a second well bore pattern in the form of a second substantially quadrilateral area. The second well bore pattern also extends from the surface well bore. The first and second well bore patterns are arranged such that a first side of the first quadrilateral area is disposed substantially in common with a first side of the second quadrilateral area.
In accordance with another embodiment of the present invention, a system for accessing a subterranean zone from the surface includes a surface well bore extending from the surface to the subterranean zone. The system also includes a plurality of well bore patterns disposed within the subterranean zone each extending in a different direction from the surface well bore. The plurality of well bore patterns are symmetrically disposed about the surface well bore.
In accordance with yet another embodiment of the present invention, a method for accessing a subterranean zone from the surface includes forming a first well bore pattern extending from a first surface well bore and disposed within the subterranean zone. The method also includes forming a second well bore pattern extending from a second surface well bore and disposed within the subterranean zone. The first and second well bore patterns are arranged to nest adjacent each other within the subterranean zone.
Technical advantages of the present invention include providing an improved method and system for accessing subterranean zones from a limited area on the surface. In one embodiment, a plurality of well bore patterns are drilled in a target zone from a common articulated surface well in close proximity to a corresponding number of cavity wells. The well bore patterns are interconnected to the cavity wells through which entrained water, hydrocarbons, and other fluids drained from the target zone can be efficiently removed and/or produced. As a result, gas, oil, and other fluids from a large, low pressure or low porosity formation can be efficiently produced at a limited area on the surface. Thus, gas may be recovered from formations underlying rough topology. In addition, environmental impact is minimized as the area to be cleared and used is minimized.
Yet another technical advantage of the present invention includes providing an improved method and system for preparing a coal seam or other subterranean deposit for mining and for collecting gas from the seam after mining operations. In particular, cavity wells and an articulated well are used to degasify a coal seam prior to mining operations. This reduces both needed surface area and underground equipment and activities. This also reduces the time needed to degasify the seam, which minimizes shutdowns due to high gas content. In addition, water and additives may be pumped into the degasified coal seam through the combined well prior to mining operations to minimize dust and other hazardous conditions, improve efficiency of the mining process, and improve the quality of the coal product. After mining, the combined well is used to collect gob gas. As a result, costs associated with the collection of gob gas are minimized to facilitate or make feasible the collection of gob gas from previously mined seams.
Another technical advantage of the present invention includes a system and method for enhanced access to subterranean zones from a limited surface area by nesting well bore patterns within the subterranean zone. For example, in one embodiment of the present invention, each well bore pattern may be formed to access a generally quadrilateral configured area of the zone. Two or more of the well bore patterns may then be nested together to provide uniform and optimum coverage of the zone. Additionally, each nested well bore pattern may be formed from two or more well bore sub-patterns. The well bore sub-patterns generally comprise two or more discreet well bore patterns in communication with a common surface well bore. Thus, a variety of different shaped well bore patterns may be formed and nested together to obtain uniform and optimum coverage of a particular subterranean zone.
Other technical advantages of the present invention will be readily apparent to one skilled in the art from the following figures, description, and claims.